1. Field of the Invention
The present invention relates to a resist material and an exposure method for, for example, microfabrication in the field of semiconductor.
2. Description of Related Art
In the field of semiconductor, for example, with the improvement in the degree of integration of semiconductor devices, there is an urgent need to establish a new process technique allowing the processing of an ultra-fine pattern on the order of, for example, 0.1 μm or less.
For the fine pattern processing, a so-called lithography technique is indispensable. In order to realize the ultra-fine processing, lithography techniques utilizing a g-line and an i-line emitted from a conventional mercury lamp or an ultraviolet light emitted from a KrF (Krypton-Fluoride: wavelength of 248 nm) excimer laser and an ArF (Argon-Fluoride: wavelength of 193 nm) excimer laser have been applied in the industry to reduce a wavelength of exposure light so as to improve an optical resolution. These techniques are applied only to the fabrication of devices according to a design rule of 0.13 μm or more because of the limitation of resolution due to the utilized wavelength.
Thus, there is a pressing need to develop a new lithography technique which allows fabrication of devices according to a design rule of 0.1 μm or less. For this purpose, the development of a new exposure technique using a vacuum ultraviolet (hereinafter, abbreviated as VUV) light having a wavelength of 170 nm or less has been energetically advanced. The VUV light has a further shorter wavelength than that of an exposure light emitted from the light source which has been used in conventional lithography techniques. As a specific light source, the development of a lithography technique using an F2 (fluoride dimer) excimer laser (wavelength: 157 nm) is advanced as a successor technique of the existing ArF lithography. Furthermore, as a successor technique of an F2 lithography, a lithography technique using an Ar2 (argon dimer) excimer laser (wavelength: 126 nm) has been proposed.
In the wavelength range of the above VUV light, however, normal organic materials which are conventionally used as resist materials exhibit a high optical absorbance. Accordingly, there arises a problem in that radiated light does not reach the lower portion of a resist layer, failing to form a good rectangular resist pattern. As a result, the resist pattern is degraded. More specifically, since resins such as novolac resins (for i-line lithography), polyhydroxystyrene resins (for KrF lithography) and acrylic resins (for ArF lithography), each of which serves as a main skeleton of a polymer constituting the existing resist material, have a high absorbance in the VUV light range. Therefore, such resins cannot be used as resist materials for VUV lithography.
Thus, as a conventional measure for dealing with the degradation of the resist pattern, a transmittance of the entire resist layer has been improved by reducing a thickness of the resist film to about 70 nm or less. However, such a measure has disadvantages in that a sufficient etching resistance cannot be obtained for the reduced thickness of the resist film and in that the number of defective resist layers is increased due to the reduction in thickness.
As another measure for coping with the degradation problem of the resist pattern, a surface imaging method along with a silylation reaction and the like has been employed. Although the surface imaging method has a low transmittance, it enables the patterning. However, the surface imaging method has disadvantages in that an edge roughness of a resist pattern occurs remarkable and in that the dimension control is not sufficient.